The present invention relates to control of the level of moisture in grain dryers, and to automated or semi-automated moisture controllers used in grain dryers, such as in continuous flow corn dryers. More particularly, the present invention relates to methods and structures for retrofitting existing grain dryers with a control system to regulate the grain dryer to operate to a desired level of moisture in the dried grain.
Freshly harvested grain frequently requires some degree of drying prior to storage to prevent spoilage, and grain dryers are well known in the agricultural arts. In these grain dryers, the removal of too little moisture doesn't adequately preserve the grain, but the removal of too much moisture not only wastes fuel but also can result in excess shrinkage and lightening of the grain. Additionally, the initial moisture of the grain is not always constant, but rather can change from time to time and in different grain samples. Accordingly, many grain dryers include control systems which can adjust the amount of moisture taken out of the grain based upon sensed measurements of the grain. Examples of prior art control systems for grain dryers can be found in U.S. Pat. Nos. 3,946,496, 4,249,891, 4,599,809, 4,750,273, 5,144,755, 5,189,812, 5,570,521, 5,651,193, 6,318,000 and 6,834,443, all incorporated by reference.
Some older moisture controllers in continuous flow corn dryers are temperature based systems. In such older temperature-based systems, when the grain rises to a selected temperature, the grain is presumed to have dried down to the desired moisture content. With these prior art temperature-only based drying systems, a major problem is drying a commodity with a small moisture point removal or small moisture differential being achieved. An example would be if corn comes in from the field at less than 20 percent moisture, with the desired unload moisture being a 15.5 percent moisture content. The grain will not rise to a high enough column temperature to allow the temperature-based system to control the unload system accurately without producing an over-dried product. The prior art temperature-based system thus wastes liquid propane, natural gas and/or electricity in the process, and results in a lower-than-desired final product test weight per volume.
More modern moisture sensing systems (presently marketed by companies such as GSI, Farm Fans (Dry-Tek), Miller and Sukup) include a moisture sensor, which can be calibrated or corrected with a grain temperature measurement. Electrical readings from the sensors are read and interpreted by a controller/processor. One or more metering rolls are located within the grain pathways, driven by a metering roll motor. Based upon measurements taken during the drying process, the controller governs the metering roll motor speed so the grain leaving the grain dryer is at the desired moisture content.
While the modern grain dryers and control systems are beneficial, they have significant limitations and problems. The humidity sensors used are often difficult to keep accurate, with the accuracy problems being exacerbated due to the debris that comes from the commodity or corn. As the commodity gets augured past the sensors, the direction of grain flow will take grain and impurities across the sensor. Cornstalks, cobs and other impurities that come through the dryer can hang up on the sensor or sensor fin due to long stalks or moisture from the drying process. Bees wings or other airborne matter can also build up and stick to the sensor. This build up can change the readings that the sensors/sensor fins receive. When inaccurate sensor readings are provided to the controller/processor, the system will ultimately unload the dryer at an inaccurate speed. The problem will persist if the sensors or sensor fins are not cleaned daily (or more often), which often does not occur in the field.
Cold temperatures outdoors can also keep sensors from giving accurate readings. One known solution to the cold temperature problem is to wrap the sensor, located in the bottom of an auger, with insulation when the outdoor temperature is at or lower than around 15° F. The warmth from the exiting grain warms up the sensor enough to give accurate readings at the controller/processor.
A more pervasive problem with modern grain dryers and control systems stems from the fact that improvements to the control systems are usually made by the same company selling the grain dryer itself, and the control systems improvements are used to market new grain dryers. Grain dryer manufacturers have little incentive to produce systems that will last for decades, when they would rather sell new grain dryers with the latest and greatest control system. Control systems are usually designed and installed as part of the original equipment grain dryer, with little thought put into repair or replacement of the control system, and with little consideration given to use of older grain dryers with malfunctioning or archaic control systems or without any control system in place. Better solutions are needed, particularly for retrofitting older grain dryers in the field or improving the control systems that exist in the field.